Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with agraphical user interface showing our new design; and,

FIG. 2 is an enlarged view of a portion taken from FIG. 1.

The broken lines shown in the drawings represent portions of the displayscreen or portion thereof with a graphical user interface that form nopart of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.